Telecommunication cable including optical fiber module

ABSTRACT

A telecommunication cable includes a plurality of modules, each with a thin retaining sheath for clamping optical fibers together. Each retaining sheath contains plural respective modules and is mechanically coupled to the retaining sheaths of the respective modules to form supermodules that contact an outside jacket. The retaining sheath of a supermodule includes an identification color or line to distinguish the supermodules from each other.

REFERENCE TO RELATED APPLICATION

This application relies for priority on the PCT InternationalApplication No. PCT/FR01/02953, filed Sep. 21, 2001, which is based onthe French Application No. 00-12966, filed Oct. 9, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a telecommunication cable includingoptical fiber modules. For example, the cable is a monomode fiber cablefor transmitting high bit rate telephone and/or computer signals, inparticular in a local area network or between telephone central officesor other switching or routing systems.

2. Description of the Prior Art

U.S. Pat. No. 5,155,789 discloses a telecommunication cable consistingof a plurality of optical fibers disposed in a jacket and divided intomodules each enclosed in a thin retaining sheath that is easy to tear.The retaining sheaths hold the modules together and are in contact withthe optical fibers to clamp them together without decoupling the opticalfibers. The jacket, which may have an inner layer, which is preferablyextruded, and a second layer which is outer and provides the finishedpresentation of the cable, is in contact with the module retainingsheaths to constitute a compact assembly.

The number of optical fibers in the above kind of cable can be verylarge, and can exceed a few hundred or even a few thousand. This highnumber of fibers gives rise to practical problems, especially whenconnecting the ends of the optical fibers in one cable to the ends ofoptical fibers in one or more other cables. The number of differentcolors used for the module retaining sheaths is typically limited toaround twelve. Consequently, if the cable comprises a very large numberof optical fibers divided into modules with from three to around twelvefibers per module, for example, the cable includes several modules ofthe same color. The low number of retaining sheath colors makes itdifficult to identify the modules and to fan them out and assemble theminto subassemblies respectively to be connected to other cables, and canlead to connection errors.

OBJECT OF THE INVENTION

The present invention aims to solve the practical problems referred toabove and in particular to facilitate fanning out the optical fibers andidentifying them in a telecommunication cable containing a very largenumber of sheathed optical fiber modules.

SUMMARY OF THE INVENTION

Accordingly, a telecommunication cable including a plurality of moduleswhich each have a thin retaining sheath clamping optical fiberstogether, and a jacket around the modules is characterized in that itcomprises retaining sheaths which each contain a plurality of respectivemodules and each of which is mechanically coupled to the retainingsheaths of the respective modules to form supermodules in contact withthe jacket, and the retaining sheath of each supermodule includesidentification means for distinguishing the supermodule from othersupermodules in the cable.

By assembling the modules into supermodules identified by supermoduleretaining sheaths different the one to the others, the groups of modulesrespectively contained in the supermodules can be fanned out separately.Because the number of supermodules in the cable, which is of the orderof twelve, for example, is significantly lower than the number ofmodules, the supermodule identification means of the supermodules aredifferent from each other. This prevents confusion between moduleretaining sheaths of the same color respectively included insupermodules.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will become moreclearly apparent on reading the following description of preferredembodiments of the invention, given with reference to the correspondingaccompanying drawings, in which:

FIG. 1 is a highly enlarged diagrammatic perspective view of asupermodule conforming to the invention and containing six optical fibermodules; and

FIG. 2 is a highly enlarged sectional view of a cable containing foursupermodules conforming to the invention.

DETAILED DESCRIPTION OF THE DRAWING

As shown in FIG. 1, a supermodule SM included in a telecommunicationcable according to the invention includes a plurality of optical fibermodules MO, for example six modules, and more generally at least twooptical fiber modules MO. The relatively small number of modules MO inthe supermodule SM enables the modules to be clearly distinguished fromeach other. For example, the retaining sheaths 3 of the modules in eachsupermodule are different colors.

In a manner that is known from U.S. Pat. No. 5,155,789, each module MOincludes a plurality of optical fibers 1-2 each having a silica core 1coated with a colored identification layer 2 and a thin retaining sheath3 which is easy to tear and holds the fibers 1-2 together. The layers 2of fibers in the module MO are different colors. The retaining sheath 3,called as “microgaine” (μGaine (registered trade mark)), is in contactwith the optical fibers and is mechanically coupled to the opticalfibers to clamp them together. This coupling means that a traction forceexerted on the retaining sheath 3 moves the optical fibers 1-2 containedin the sheath in translation at the same time and conversely that atraction force exerted on the fibers moves the retaining sheath intranslation at the same time. The coupling ensures cohesion of theretaining sheath and the fibers that it contains and makes the moduleformed in this way highly compact.

As shown in FIG. 1, for example, a module MO comprises 3 to 12 opticalfibers. The retaining sheaths 3 of the modules MO are adapted to thecharacteristics of the constituent materials of the optical fibers sothat they clamp them and couple them so that expansion and contractionforces due to temperature variations are very much lower than stressesthat could degrade the optical fibers. The fact that the retainingsheaths 3 are thin avoids subjecting the fibers 1 to tension andcompression stresses during thermal cycling.

The supermodule SM also includes a retaining sheath 4 surrounding all ofthe respective modules MO contained in the supermodule to group them andhold them together. The sheath 4 is in contact with the retaining sheath3 of each module MO and is mechanically coupled to the retaining sheaths3 of the modules so as to clamp them. The thickness of the sheath 4 isat most about a few tenths of a millimeter, typically from 0.1 mm to 0.5mm.

Like the material of the retaining sheaths 3 of the modules MO, thematerial of the sheaths 4 of the supermodule SM is an amorphousthermoplastic material, for example polyvinyl chloride (PVC), or anelastomer; or a thermoplastic material, for example a polyethylene, apolypropylene, or a polyolefin, such as ethylene vinyl acetate (EVA),and possibly contains one or more of the following mineral fillers:chalk, kaolin, silica, talc, calcium carbonate, alumina hydrate ormagnesium hydrate, titanium oxide. The material of the retaining sheath4 of the supermodule SM is preferably installed by extrusion around therespective set of modules MO simultaneously with drawing and assemblingthe modules MO and simultaneously with drawing and assembling theoptical fibers 1-2 in the modules MO, the assembly operations preferablyapplying a twist in periodically alternating directions.

A filler material 5 fills the interior of the retaining sheath 3 of eachmodule MO between the optical fibers 1-2 contained in the module. Thefiller material 5 is a sealing product such as silicone or syntheticgrease, oil or gel, with which the optical fibers are coated before theyare passed through a die for extruding the retaining sheath 3 of themodule. To enhance the lengthwise seal inside the cable, the fillermaterial 5 fills all of the space between the modules MO and theretaining sheath 4 of the supermodule SM, the modules MO being coatedwith the material 5 as they pass through a die for extruding the sheath4.

In other embodiments, the filler material 5 is produced “dry” byassociating swelling powder and/or swelling filaments and/or swellingtapes that swell in the presence of water to form a stopper thatprevents propagation of water between, on the one hand, the opticalfibers 1-2 inside the retaining sheath 3 of each module MO and, on theother hand, between the modules MO inside the retaining sheath 4 of thesupermodule SM.

Referring now to FIG. 2, a telecommunication cable CA according to theinvention includes at least two supermodules SM, and more generally aplurality of supermodules SM, of which there are four in the exampleillustrated.

The supermodules SM are grouped together in an outer cable jacket 6-7 incontact with the retaining sheaths 4 of the supermodules to form acompact assembly. The outer jacket 6-7 is preferably made up of one ormore extruded layers, at least one of which preferably includes buriedor extruded mechanical reinforcements and/or tapes. In the example shownin FIG. 2, the outer jacket 6-7 has an inner layer 6 in contact with theretaining sheaths 4 of the supermodules SM, and an outer layer 7 thickerthan the inner layer 6.

As in the supermodules SM and the modules MO, the filler material 5preferably fills all of the space between the supermodules SM inside thecable jacket 6-7 to improve further the sealing of the cable.

The retaining sheath 4 of each supermodule SM includes respectiveidentification means for identifying the supermodule and distinguishingit from the other supermodules contained in the cable CA, especiallywhen fanning out the supermodules SM and the modules MO for connectingthe ends of the fibers 1-2.

In a first embodiment, the retaining sheath 4, serving as identificationmeans, includes a colored external identifying film coating from a fewthousandths of a millimeter to a few tenths of a millimeter thick, likethe retaining sheaths 3 for the optical fibers 1-2. As an alternative tothis, the colored external film coating is replaced by integral coloringof the sheath 4. At least the outside faces of the sheaths 4 of thesupermodules are then different colors.

In a second embodiment, which is shown in FIG. 1 and can be combinedwith the first embodiment, the supermodule identification meanscomprises one or more lines or strips 8 which are predetermineddifferent colors from each other and in respect to the sheath 4. Moregenerally, the colors of the lines 8 of each supermodule are differentfrom the colors of the lines of the sheaths 4 of the other supermodulesSM in the cable CA. The colored lines 8 extend longitudinally orhelically along the sheath 4, and are either extruded simultaneouslywith the extruded sheath 4 or printed on the sheath 4, for example usingindelible paint or ink. The lines 8 are narrow and can be significantlyproud of the outside surface of the sheath 4.

In a third embodiment, also shown in FIG. 1, the identification means ofthe supermodule SM comprises a mark or sign made up of alphanumericcharacters, such as SMX, in which X is the number of the supermodule,for example, which is marked on the sheath 4, preferably periodicallyand longitudinally and/or helically on the sheath. Like the line orlines 8, the mark SMX is preferably fluorescent so that it is morevisible in low light.

In an analogous manner to the optical fibers 1-2 in the modules MO andthe modules MO in the sheaths 4 of the supermodules SM, the retainingsheaths 4 are made simultaneously with drawing and assembling the SZtwisted modules MO. The supermodules SM are preferably extruded on an SZextrusion line and are therefore twisted together with opposite andalternating twisting directions, i.e. having alternate sections with aforward helix pitch and then a retrograde helix pitch.

1. A telecommunication cable including: a plurality of modules, eachhaving a thin retaining sheath for clamping optical fibers together; aplurality of supermodules, each having a thin retaining sheath thatincludes a plurality of respective modules, each supermodule retainingsheath being mechanically coupled to said retaining sheaths of saidrespective modules, said mechanical coupling of each supermoduleretaining sheath to said respective module sheaths being as a result ofan extrusion of said supermodule sheath around said modules; a jacketaround and in contact with said retaining sheaths of said supermodules;and an identifier included respectively in said retaining sheaths ofsaid supermodules for distinguishing each supermodule from the othersupermodules in said cable.
 2. A cable according to claim 1, whereinsaid retaining sheaths of the supermodules are made simultaneously withdrawing and assembling of said modules.
 3. A cable according to claim 1,wherein said supermodules are twisted in opposite and alternatingtwisting directions.
 4. A cable according to claim 1, wherein saidretaining sheath of each supermodule has a thickness of more than abouta few tenths of millimeter.
 5. A cable according to claim 1, whereinsaid retaining sheaths of said supermodules consist of the same materialas said retaining sheaths of said modules.
 6. A cable according to claim1, wherein the material of said retaining sheaths of said supermodulesis selected from the group consisting of an amorphous material, anelastomer and a thermoplastic material.
 7. A cable according to claim 1,wherein said identifier included respectively in said retaining sheathsof said supermodules have colors different from one of the others.
 8. Acable according to claim 1, wherein said identifier includedrespectively in said retaining sheaths of said supermodules havedifferent colors from one of the others at least for outside faces ofsaid retaining sheaths of said supermodules.
 9. A cable according toclaim 1, wherein said identifier included in said retaining sheath ofeach supermodule comprises at least colored lines having differentcolors from one of the others and in respect to said retaining sheath ofsaid each supermodule.
 10. A cable according to claim 1, wherein saididentifier included in each supermodule comprises a mark markedperiodically on said retaining sheath of said each supermodule.
 11. Acable according to claim 1, wherein said retaining sheaths of saidmodules in each supermodule have different colors from one to theothers.
 12. A cable according to claim 1, wherein said jacket comprisesat least an extruded layer.
 13. A cable according to claim 12, whereinsaid extruded layer includes mechanical reinforcements.
 14. A cableaccording to claim 1, comprising a sealing product filling at least aspace between said retaining sheaths of said supermodules inside saidjacket.